I used to own parakeets, never had one die on me. However, when I returned to college, I re homed it. When I graduated and moved into my own home, I , also had parrots for a time, before health issues forced me to re-home them, too. I no longer will keep birds because I hated having to let them go.
The point of this all was that I did a lot of research before bringing these animals into my home, and as people have mentioned...a lot of things can cause death.
Here is a list of some common household items that are toxic:
http://www.plannedparrothood.com/plants.html
Here is another list...
http://www.parrot-and-conure-world.c...for-birds.html
Here is information on Teflon toxicity:
http://www.peteducation.com/article....+1829&aid=2874
A little research may pinpoint your particular issue as I have no clue what you have in your home, and what you don't.
Sorry to hear of the little fellows passing.
Good luck!